1. Field of the Invention
The present invention relates to a snow tire and brake pins therefor for use on automobiles or vehicles which are used for land travel in cold areas.
2. Description of Related Arts
Heretofore, spike tires have been used widely as a special equipment tire for use during winter seasons for vehicles for transportation (i.e., automobiles) intended to be run in snowy or cold areas.
FIG. 15 is a perspective view of a spike tire before brake pins (spike pins) are fitted thereto.
FIGS. 16 and 17 are a transverse section and a longitudinal section, respectively, of a conventional spike tire, and FIGS. 18 through 20 are a plan view, sectional side view, and perspective view, respectively, of an example of a spike pin used for the conventional spike tire.
As shown in FIGS. 16 and 17, existing spike tires 10 generally include basic rubber tires which have a plurality of metal spike pins 11 uniformly spaced apart and embedded radially in the road engaging surface of the tread such that the tips 12 of the respective spike pins 11 are protruding slightly out of the road-engaging surface of the tire. Usually, the tips 12 are provided with a protective member made of super hard alloy so as to prevent the wear of the pins. The spike tires of the above-described construction have been felt indispensable by most drivers for assuring traffic safety during winter seasons in cold areas because they can avoid slipping while the automobile is being driven, with the spike pins 11 thrusting into the pressed snow surface or icebound surface on the road.
Recently, however, there has arisen a serious problem for society in that a large amount of dust is formed due to the use of spike tires, and to the rapid increase in the amount of traffic in towns and cities. This is based on a phenomenon that when vehicles equipped with spike tires run on a paved road which is not covered with snow, the tips 12 of the spike pins cut or scrape the pavement material such as asphalt or concrete to form fine particles thereof or dust which then are scattered and float in the air. Dust is formed very often and in large amounts particularly at the change of season, for example, from autumn (fall) to winter or from winter to spring in towns and cities where there is much traffic, and the amount of dust formed increases greatly year after year. Thus, it is now feared that formation of dust by the use of spike tires has significant impact on the health of urban inhabitants.
In order to avoid pollution of the environment with dust, there would seem to be no choice but to completely prohibit people from using spike tires. In fact, the use of spike tires is prohibited completely by the authorities in some countries.
In Japan, efforts are being made by the authority to promote the use of tires of a new type which can create a braking effect by using rubber only. The new tires are called studless or non-spike tires. However, the new tires do not seem as excellent in the performance of braking or driving as had been expected or advertised by the manufacturers. And, there is strong desire among professional drivers such as drivers of hired cars, taxis, trucks and the like that the use of conventional spike tires which have excellent braking performance be allowed in future, even for a limited period of time such as for several years.
New tires such as studless tires and snow tires, which are being put into use presently, are designed to improve braking power by using a basic tire made of a soft rubber of a special composition and provided with grooves of a sophisticated shape or pattern on its road-engaging surface. These tires are said to exhibit braking power of only about 30% of that given by the conventional spike tires when the vehicle equipped with this type of tires is driven on a hard pressed snow surface such as one after melting and refreezing or an icebound road. This would strongly suggest that there would be a limitation in achieving sufficient braking performance by using only rubber.
After intensive investigation in respect to such new tires, the present inventor has reached a conclusion that in order to assure the same level of braking performance or driving performance as the conventional spike tires 10, it is necessary to use a member or part which can serve as something like claws in a limb or paw of animal. However, this claw-like part or member should not scrape the pavement. To explain the conventional spike tires 10 in detail, spike pins 11 are radially embedded or implanted in a rubber tire in a uniformly spaced apart fashion (FIGS. 16 and 17). Since the spike pins 11, which are made of a metal, one of non-elastic material, are present in rubber, one of an elastic material, and the tips of the spike pins are provided with a super hard alloy protector, the rubber is worn out and the spike pins 11 come out of the rubber, i.e., protrude from the surface of the tire after its repeated use or after driving of the vehicle for a long period of time. In this state, the spike pins 11 scrape a larger amount of pavement, resulting in the formation of more dust. This mechanism could be ascribable to the use of spike pins 11, i.e., metal pins. However, this assumption is not justified.
In the previous investigation, the present inventor has also found that the formation of dust is not caused by the mere fact that spike pins 11 are made of a metal or they are provided with a super hard alloy protector at their tips 12, but dust is formed because spike pins 11 are used alone. In other words, the cause of formation of dust is not what material is used but instead what structure the spike pin 11 has.
According to the previous proposal by the present inventor (Japanese Utility Model Publication (Kokai) No. 67305/1988), the spike pins which are designed to have a resilient structure are embedded radially in a studless tire so that they can absorb resilient deformation of the rubber tire. By this construction, the spike tire can prevent the occurrence of damages on the paved road and thus the formation of dust while maintaining its braking performance in the case of driving the vehicle equipped with the tire on icebound or snow-covered paved-road is as high as the breaking performance of conventional spike tires. More particularly, the tire includes brake pins which each have a hard flange in the form of a circular plate to which are fixed as a bundle plural (e.g., 5 to 10) pins of U-shaped steel wire rod covered with a wrapping rubber such that the forks of the U-shaped pins pierce into the wrapping rubber until the flange comes in contact with the wrapping rubber. Studless tires of a structure in which the above-described brake pins are embedded radially in the rubber tire so that the tips of the pins are on the same level as the road-engaging surface of the tire can effectively prevent slipping due to the effects of flexible rubber of the studless tire and unique construction which sharp tips of the brake pins made of wire rod have, thus exhibiting sufficient braking power when the vehicle equipped with the studless tire of this type is run on a slippery hard snow-covered or icebound road. On the other hand, when the tire is in contact with pavement such as asphalt or the like, the brake pins made of wire rods serve as soft resilient member for the pavement and will not damage the surface of the road since they themselves are bent.
However, the above-described brake pins are disadvantageous in that wire rods are implanted in hard flanges made of hard synthetic resin or antimony alloy using a metallic mold and therefore junction portions between the wire rod and the flange are weak and tend to cause cracks. As the result, the pins could be dropped out after continued use, which would deteriorate the impact strength of the tire.